Effect Of Actived Carbons On Mn-Based Sorbents Prepared By Supercritical Water Impregnation For Capturing H₂S From Coal Gas At Mid-Temperature

The poly-generation technology based coal gasification is now considered as one of the most promising clean coal techniques. In such systems, most of sulfur in coal will be converted to hydrogen sulphide and existed in the hot coal gas, which makes serious effects on subsequent reactions or the transport pipeline. In view of the disadvantages of "cold and hot" technology and heat loss in the process of desulfurization, hot gas desulfurization (HGD) becomes as a very important process in the gas clean up system. The dry desulfurization technology with metal oxide as active ingredients has attracted more and more attraction because of its high thermal efficiency, low energy consumption and good desulfurization effects.Supercritical water is a particulate preparation technique emerging in recent years. Metal oxide in the supercritical water has some characteristics:low solubility, high nucleation rate, conducive to the formation of ultrafine particles. The particle size as well as morphology can be adjusted by temperature, pressure and other operating parameters during hydrothermal synthesis, which could not be reached by traditional means of preparing microparticles.In this article, sub or supercritical water impregnation method was chosen to prepare manganese oxide desulfurizer loaded on activated carbon. The desulfurization effects of sorbents from different active carbon carrier prepared at different temperatures has been investigated. With the characterization methods of XRD, ICP, SEM, XANES, BET to analyze the structure, the metal content and metal valence of desulfurizers, and further to dig out the effect on the different desulfurization performance of the desulfurizers. Then the effects of temperature and activated carbon carrier on desulfurization activity of sorbent were revealed. Moreover, the influences of different pH of precursor solution on the performance of sorbent desulfurization have been also investigated. The main conclusions summarized from our paper are as follows:(1) The desulfurizers prepared with different AC carriers present a similar sulfidation trend as changing preparation temperature:350℃for the best,400℃for middle and300℃for the worst. At the same temperature, however, the Mn/AC(Z) prepared by AC from walnut skin exhibits a better sulfidation performance than that of AC(X) and AC(M) from coal.(2) Preparation temperature has a certain effect on the loading content of the active component, the higher loadings can be obtained at the higher preparation temperature. When the temperature is at400℃, the morphology of active components and carriers is slightly changed, and the desulfurization activity declined.(3) The Mn content on the desulfurizer’s surface has an obvious effect on the sulfidation performance, which increases with the increase of Mn content. However, the sulfidation performance goes against the Si content. The K and Na have no effect on the sulfidation reaction of the desulfurizer.(4) The active components contained in the desulfurizer are mainly composed of Mn3O4, meanwhile a certain amount of MnO and Mn2O3was detected, of which the distribution of Mn3O4was a key factor affecting the sulfidation performance. The higher the Mn3O4is, the better sulfidation performance it presents.(5) The sulfidation activity was remarkably affected by the pH value of the precursor solution and the sulfidation performance goes along with pH value within a certain range of1.53-7.31. When the pH reaches to8.61, sulfidation performance is declined through the formation of a yellowish-brown precipitate.